A 420 mm KOBA step gauge with gauge blocks made from tungsten carbide will be calibrated; i.e., the distances of all 22 centres of the position defining surfaces will be measured with respect to the first one (“surface zero”). The deviations to the nominal positions will be established. Uncertainties should be those reflected at the corresponding CMCs of participants (but also higher by influence of the step itself, or even smaller in case the participant wish to take this opportunity to verify new CMC equation).
This comparison follows the previous ones, EUROMET 372 (EUROMET.L-K5.PREV) and CCL.K5, regional and global one respectively.Participants from outside EUROMET are also welcome to join us.
Final Report 2012-08-24
The project has been completed ans reults are available in the KCDB.
The artefact was a step-gauge KOBA, 420 mm nominal length, steel frame, with 20 mm tungsten carbide gauges. The measurands were the distances from the centres of the front and back faces of the individual gauges of the step to the centre of the front face of the first gauge. The step-gauge should be supported in the Bessel points. The comparison involved 19 laboratories from 4 different RMOs all over the World. Comparison lasted 3 years (Dec- 2004 to Dec-2007).
A lack of stability was observed through the shifting of some of the inserted gauges. In order to save the comparison and get valuable and useful conclusions, some actions had to be taken (see Final and Executive Reports).
Conclusion: The compatibility of 18 out of 19 participants for measuring step gauges was demonstrated. Only two labs got respectively one/two anomalous values, but a high percentage (95 %) of valid values was obtained. A third lab.,with no CMC for this service, obtained only three compatible values, showing also very high systematic errors (both positive and negative).
After the comparison, some Labs. submitted to the BIPM KCDB higher CMCs for step gauges, as a result of corrective actions.